Question

1. find the interest for a principal of $4,200 at an interest rate of 2.4% for 5 months. use the simple interest formula.

interest: $_____________________
total amount:$ _____________________

1. what is the total cost of a backpack that costs $72.90 with a sales tax of 3.2?

$_____________________
in a survey of 1,800 people who owned a certain phone, 1,260 said they would buy the same phone again. what percent of the people surveyed said they would buy the phone again? use percent equation. __________ %

1. an amount of $6,500 is invested at a simple interest rate of 2%. what is the interest earned after 4 years? $

what is the total amount after 4 years?$ _____________________

1. a town’s population went from 18,500 to 22,940 in 10 years. what was the percent of change?

___________________ = ________ %

1. carlos estimated that a ribbon was 12.0 cm long. the actual length was 12.3 cm. what is the percent error of carlos’s estimate? ___________________ = ________ %

Explanation:

Problem 16

Step1: Define simple interest formula

Simple Interest formula: $I = P \times r \times t$, where $P$ is principal, $r$ is annual rate, $t$ is time in years.

Step2: Convert time to years

$t = \frac{5}{12}$ years

Step3: Calculate interest

$P = 4200$, $r = 0.024$
$I = 4200 \times 0.024 \times \frac{5}{12} = 42$

Step4: Calculate total amount

Total Amount = $P + I = 4200 + 42 = 4242$

Problem 17

Step1: Calculate sales tax amount

Tax = $72.90 \times 0.032 = 2.3328$

Step2: Calculate total cost

Total Cost = $72.90 + 2.3328 = 75.2328 \approx 75.23$

Step3: Calculate phone repurchase percent

Percent = $\frac{1260}{1800} \times 100 = 70$

Problem 18

Step1: Calculate simple interest

$I = 6500 \times 0.02 \times 4 = 520$

Step2: Calculate total amount

Total Amount = $6500 + 520 = 7020$

Problem 19

Step1: Find population change

Change = $22940 - 18500 = 4440$

Step2: Calculate percent change

Percent Change = $\frac{4440}{18500} \times 100 = 24$ (increase)

Problem 20

Step1: Find absolute error

Error = $|12.3 - 12.0| = 0.3$

Step2: Calculate percent error

Percent Error = $\frac{0.3}{12.3} \times 100 \approx 2.44$

Answer:

1. Interest: $\$42$

Total amount: $\$4242$

1. Total backpack cost: $\$75.23$

Phone repurchase percent: $70\%$

1. Interest earned: $\$520$

Total amount after 4 years: $\$7020$

1. Percent of change (increase): $24\%$
2. Percent error: $\approx 2.44\%$